Russian scientists study potential of crystalline solvates for increasing efficiency of perovskite cells

The new-found Organic-inorganic perovskites are a type of photoactive element that reacts to light. Researchers have discovered a whole group of compounds, every one of which is a crystalline solvate. These are compounds in which the molecules of the precursor components’ solvents are built into their structure. A crystalline film of perovskite is then formed from the solution of the precipitated dissolved components.

The scientists selected and observed three intermediate compounds, which are crystalline solvates of one of the two solvents most used when creating a perovskite solar battery. One of the two compounds had its crystal structure established for the first time

“We have found out that the formation of intermediate compounds is one of the key factors that determines functional properties of the final perovskite layer because perovskite crystals inherit the shape of those compounds. This, in turn, influences the film morphology and solar cell efficiency. It is especially important when creating thin perovskite films, because needle-like or filiform shape of crystals will lead to the film being discontinuous, which will significantly lower the efficiency of the solar cell,” said Ph. D., Head of Laboratory of New Materials for Solar Energetic and the principal researcher of the project Alexey Tarasov.

These intermediate compounds, however, are unstable, so the scientists used synchrotron radiation and low temperatures to cool the crystals to the temperature of -173°C. The freezing permitted the scientists to halt the decomposition of the crystals and run the necessary readings to be able to determine the structure of the solvates.
Furthermore, the scientists have researched the thermal stability of the obtained compounds and have managed to calculate the energy of their formation using quantum-chemical modelling. Knowing the formation energy allows to explain why some crystals form when using different solvents.

They also learnt that the ratio of reagents in solution specifically determines which intermediate compound will form in the process of crystallization. The shape of the perovskite crystals formed is determined by the crystal structure of the intermediate compound, which defines the structure of the light-absorbing layer. The output of the solar battery created is in turn influence by this structure.

The results of this study were published in the Journal of Physical Chemistry C.